Hitherto various attempts have been studied to give water repellency to window glasses and fender mirrors for the purpose to repel rain water and to obtain clear view in rainy days.
For example, JP-A-4-124047, JP-A-4-325446 and JP-A-5-24885 disclose coating of a silane compound containing a fluoroalkyl group R.sub.f group) on a substrate such as glass. Also JP-A-4-359086, JP-A-5-170486 and JP-A-5-213633 disclose forming of a water-repellent oxide film by partially hydrolyzing, with an acid, etc., a fluoroalkyl-containing silane compound or a metal alkoxide mixed with a fluoroalkyl-containing silane compound, condensation-polymerizing (to be sol) and then coating on a glass substrate and baking (to be gel).
However the water-repellent glass obtained by the above-mentioned methods has a problem that water-repellent groups are easy to distribute in the outermost surface of the coating film and water-repellency is lowered by abrasion. Further the fluoroalkyl-containing silane compound and its condensate have insufficient heat resistance and weather resistance, so that when used for a long period of time, they are deteriorated and cannot maintain water-repellency.
Therefore in order to solve those problems, there have been investigated various methods to obtain a water-repellent coating film by dispersing fluorine-containing resin particles having no functional group as a water-repelling component into a metal oxide obtained through so-called sol-gel method. For example, in JP-A-5-51238, JP-A-6-329442, JP-A-6-340451, JP-A-7-102207 and JP-A-7-157335, it is disclosed that a coating solution is prepared by admixing particles (powder or dispersion) of water-repellent fluorine-containing resin such as polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene polymer or fluorine-containing acrylic resin to a sol solution prepared by hydrolyzing and condensating a metal alkoxide compound in a solvent such as alcohol, and the coating solution is applied on a substrate such as glass and then baked (to be gel) to form a water-repellent coating film that the water-repellent particles are distributed in the sol-gel film.
However in those methods, though improvements of weather resistance and heat resistance can be expected, there are the following problems.
1+L Dispersion stability of fluorine-containing resin particles in the coating solution prepared by admixing the fluorine-containing resin particles to the sol solution is poor, sedimentation of the fluorine-containing resin particles easily occurs, and thus the coating film becomes turbid in white and transparency becomes lowered significantly. PA1 2+L Even if the coating solution visually seems to be dispersed, when the solution is coated and concentrated in the coating film during baking step, the fluorine-containing resin particles are coagulated because of insufficient dispersion stability, and the coating film becomes turbid in white and its transparency is lowered. PA1 3+L Since interfacial affinity between the metal oxide and the fluorine-containing resin particles is inherently low, dispersibility of the fluorine-containing resin particles in the obtained coating film is low, strength of the coating film is lowered and abrasion resistance of the coating film becomes low. PA1 (A) a fluorine-containing ethylenic polymer having functional group (hereinafter also referred to as "fluorine-containing polymer (A) having functional group") prepared by copolymerizing a fluorine-containing ethylenic monomer having functional group which has at least one functional group selected from the group consisting of hydroxyl, carboxyl, a carboxylic salt group, a carboxylic ester group or epoxy, PA1 (B-1) a metal oxide sol, and PA1 (C) a solvent. PA1 (a) 0.05 to 50% by mole of at least one of fluorine-containing ethylenic monomers having functional group and represented by the formula (1): EQU CX.sub.2.dbd.CX.sup.1 -R.sub.f -Y (1) PA1 (b) 50 to 99.95% by mole of at least one of fluorine-containing ethylenic monomers copolymerizable with the fluorine-containing ethylenic monomer (a) having functional group. PA1 (1) preparing a coating solution by mixing the metal oxide sol (B-1) and the aqueous dispersion, PA1 (2) forming a coating film by applying the coating solution to a substrate, and PA1 (3) baking the coating film to obtain the film containing the fine particles of the fluorine-containing polymer (A) having functional group in dispersed state.
4+L Since interfacial affinity between the metal oxide and the fluorine-containing resin particles in the obtained coating film is low, removal of the fluorine-containing resin particles occurs in the abrasion resistance test, and water-repellency is lowered.
As mentioned above, present situation is such that there have not yet been obtained a water-repellent coating film or water-repellent glass which is excellent in transparency and water-repellent durability such as abrasion resistance and weather resistance, and a coating composition which is used therefor and is excellent in dispersion stability.
An object of the present invention is to provide a multi-functional coating film being excellent in not only water-repellency and transparency but also stain-proofing property, non-sticking property, sliding property (abrasion resistance) and weather resistance, a method for producing the coating film, a multi-functional composite material provided with the coating film, and a coating composition which is used therefor and is excellent in dispersion stability.
Further an object of the present invention is to provide composite materials having water-repellency, stain-proofing property, non-sticking property, sliding property or weather resistance which are produced by applying the mentioned coating film on a substrate.
Also an object of the present invention is to provide a composite material for cooking apparatuses and a composite material for building.